Sheet for a thermal conductive substrate, a method for manufacturing the same, a thermal conductive substrate using the sheet and a method for manufacturing the same

ABSTRACT

A thermally conductive substrate having a structure in which inorganic filler for improving the thermal conductivity and thermosetting resin composition are included. The thermosetting resin composition has a flexibility in the not-hardened state, and becomes rigid after hardening. The thermally conductive substrate has excellent thermal radiation characteristics. The method of manufacturing the thermally conductive substrate includes: piling up (a) the thermally conductive sheets comprising 70 to 95 weight parts of an inorganic filler, and 4.9 to 28 weight parts of a thermosetting resin composition, the thermosetting resin composition comprising at least one thermosetting resin, a hardener and a hardening accelerator, and (b) lead frame on which a wiring is formed; thermal pressing the pile; filling the thermally conductive sheet to the surface of the lead frame; hardening the thermosetting resin; cutting excess sections of the thermally conductive substrate; and processing the bending perpendicularly for making a removable electrode.

FIELD OF THE INVENTION

[0001] The invention relates to a circuit substrate whose thermalradiation property is improved by a mixture of resin and inorganicfiller. In particular, it relates to a high thermal radiation printedwiring board made of resin (thermally conductive substrate) for mountingelectronic power devices.

BACKGROUND OF THE INVENTION

[0002] Recently, as high performance and miniaturization of theelectronic apparatus have been required, high density and highperformance semiconductors have been sought. Consequently, circuitsubstrates for mounting thereof have also been required to be small andof high density. As a result, it is important to design circuitsubstrates taking the thermal radiation property into consideration. Awell known technique for improving the thermal radiation property ofcircuit substrates, while using a printed circuit board made ofglass-epoxy resin, is to use, a metal base substrate having a metal, forexample, aluminum etc. and form a circuit pattern on one face or bothfaces of this metal substrate with an insulating layer interposed inbetween the circuit pattern and the metal substrate. Moreover, whenhigher thermal conductivity is required, the metal base substrate ismade of a copper plate, which is directly bonded to a ceramic substratemade of, for example, alumina or aluminum nitride. For an applicationrequiring relatively small electric power, a metal base substrate isgenerally used. In this case, however, in order to improve the thermalconduction, the insulating layer must be thin. Therefore, as for thesubstrate of thin insulating layer, break down voltage is low, and theinfluence by the noise, too, is big.

[0003] It is difficult for the metal base substrate and ceramicsubstrate to satisfy both performance and cost requirements. Recently,an injection molded thermally conductive module has been suggested,where a thermoplastic resin composition containing inorganic filler isintegrated with the lead frame of an electrode. This injection moldedthermally conductive module has excellent mechanical strength incomparion with a ceramic substrate. However, due to the high viscosityof the thermoplastic resin, it is difficult to injection mold such amodule with a high filler content, and so the thermal radiation propertyof module is poor. In particular, at the time of melting thethermoplastic resin at high temperature and kneading with filler, ifthere is too much filler, the melting viscosity is rapidly increased ina point that not only kneading but also injection molding is madeimpossible. Moreover, the filler serves as an abrasives to abrade themetallic mold, and, thus, reduces the life of the mold. Consequently,the content of the filler is limited, so that only lower thermalconductivity can be obtained as compared with the thermal conductivityof the ceramic substrate.

SUMMARY OF THE INVENTION

[0004] The object of the present invention is to overcome the abovementioned problems and to provide a sheet for a thermally conductivesubstrate in which an inorganic filler can be filled in a resin at ahigh filler loading to form a thermally conductive module by a simplemethod, having (a) approximately the same coefficient of the thermalexpansion in the plane direction of the substrate as that of asemiconductor, and (b) excellent thermal radiation property; a methodfor manufacturing the above mentioned sheet for a thermally conductivesubstrate; a thermally conductive substrate using the above mentionedsheet; and a method for manufacturing this thermally conductivesubstrate.

[0005] In order to attain the objects, the sheet for the thermallyconductive substrate of the present invention is a sheet mixturecomprising 70 to 95 weight parts of inorganic filler and 5 to 30 weightparts of resin composition comprising at least thermosetting resin,hardener and hardening accelerator. This sheet mixture has a goodflexibility in the half hardened state or partially hardened state.(Hereinafter, “B stage” will be used for the half hardened state orpartially hardened state.) This sheet mixture of the thermallyconductive substrate can be molded and processed into a predeterminedshape due to the flexibility of the sheet. On complete hardening of theresin composition, the substrate can be made rigid with excellentmechanical strength.

[0006] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the half hardened state orpartially hardened state has a viscosity in the range of 10² to 10⁵(Pa·s). By such a preferred embodiment, excellent flexibility andprocessing property can be provided, so that the sheet can be molded andprocessed into the predetermined shape. More preferably, the halfhardened state or partially hardened state has a viscosity in the rangeof 10³ to 10⁴ (Pa·s). The viscosity of the sheet herein is measured bythe following method: the apparatus used for measuring theelasto-viscosity was a “cone and plate” type dynamic measurementapparatus. MR-500, the product of Rhelogy Co., Ltd.; the sheet wasprocessed into the predetermined size and sandwiched between the coneand plate having a diameter of 17.97 mm and cone angle of 1.15 deg.;sinusoidal oscillation was given to the sample in the twistingdirection; and the difference in the phases of torque which wasgenerated by the sinusoidal oscillation was calculated. Thus, theviscosity was measured. In the evaluation of the elasto-viscosity of thesheet of the present invention, the sinusoidal oscillation was a sinewave with a frequency of 1 Hz, the strain was 0.1 deg., the load was 500g and the temperature was 25° C.

[0007] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that 0.1 to 2 weight parts of solventhaving a boiling point of not less than 150° C. is further added to 100weight parts of total weight of inorganic filler and thermosetting resincomposition. By this preferred embodiment, excellent flexibility andprocessing property can be provided.

[0008] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the solvent having a boilingpoint of not less than 150° C. is at least one solvent selected from thegroup consisting of ethyl carbitol, butyl carbitol and butyl carbitolacetate. By this preferred embodiment, the processing of the sheetmaterial is easy, flexibility can be provided to the thermosetting resinat room temperature, and the viscosity of the sheet material for moldingand processing can easily be controlled.

[0009] It is preferable in the thermosetting resin composition in thesheet for the thermally conductive substrate of the present invention tocomprise:

[0010] 1) 0 to 45 weight parts of a first resin that is solid at roomtemperature,

[0011] 2) 5 to 50 weight parts of a second resin that is liquid at roomtemperature,

[0012] 3) 4.9 to 45 weight parts of the hardener, and

[0013] 4) 0.1 to 5 weight parts of the hardening accelerator when thethermosetting resin composition is 100 weight parts. By such a preferredembodiment, excellent flexibility and processing property can beprovided.

[0014] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the main component of thethermosetting resin that is solid at room temperature is one or morecomponents selected from the group consisting of bisphenol A epoxyresin, bisphenol F epoxy resin and liquid phenol resin. By thispreferred embodiment, the “B stage” resin has a long shelf life and thehardened resin has excellent electrical insulating property andmechanical strength.

[0015] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the main component of thethermosetting resin composition is at least one resin selected from thegroup consisting of epoxy resin, phenol resin and cyanate resin.

[0016] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the thermosetting resincomposition comprises brominated multifunctional epoxy resin as a maincomponent, bisphenol A novolak resin as a hardener, and imidazole as ahardening accelerator. By such a preferred embodiment, the substrate canbe made excellent in flame retardant property, electric insulatingproperty and mechanical strength.

[0017] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the brominated multifunctionalepoxy resin be in the range of 60 to 80 weight parts; bisphenol Anovolak resin as a hardener be in the range of 18 to 39.9 weight parts,and imidazole as a hardening accelerator be in the range of 0.1 to 2weight parts.

[0018] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the inorganic filler is at leastone kind of filler selected from the group consisting of Al₂O₃, MgO, BNand AlN, because these fillers are excellent in thermal conductivity.

[0019] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that at least one additives isselected from the group consisting of coupling agent, dispersing agent,coloring agent and tack free agent is further added to the sheet for athermally conductive substrate.

[0020] Next, the thermally conductive substrate of the present inventionis characterized in that when the thermosetting resin component of thethermally conductive substrate sheet is hardened, the coefficient ofthermal expansion is in the range of 8 to 20 ppm/° C. and the thermalconductivity is in the range of 1 to 10 W/mK. In the thermallyconductive substrate, thermal deformation or the like is not generatedand the coefficient of thermal expansion approximates that of asemiconductor.

[0021] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the flexural strength of thethermally conductive substrate is not less than 10 Kgf/mm². If theflexural strength is within the above mentioned range, practicalmechanical strength can be obtained. The flexural strength herein ismeasured according to JIS R-1601 (the testing method of bending strengthof fine ceramics) in the following manner: test sample is cut in apredetermined size; the test sample is placed on two supporting pointswhich are located at certain distance; load is applied to the middlepoint of the test sample between two supporting points; the maximumbending stress when the test sample breaks is measured and this value isdefined as flexural strength. This value is also called the three-pointbending strength.

[0022] The dimensions of the test sample are as follows:

[0023] Whole Length (Lr): 36 mm

[0024] Width (w): 4.0±0.1 mm

[0025] Thickness (t): 3.0±0.1 mm

[0026] The bending strength is calculated by the following equation:

σ=3PL/2 wt²

[0027] wherein σ denotes the three-point bending strength (kgf/mm²), Pdenotes the maximum load when the test piece is broken, L denotes thedistance between lower supporting points (mm), w denotes the width ofthe test piece (mm) and t denotes the thickness of the test piece (mm).

[0028] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the flexural strength is in therange of 10 to 20 Kgf/mm².

[0029] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that a lead frame is furtherintegrated to the thermally conductive substrate, and the thermallyconductive substrate is filled to the surface of the lead frame. By sucha preferred embodiment, electronic parts can easily be attached to thelead frame and thermal resistance for connecting thermal radiation canbe inhibited. Moreover, soldering terminals for connecting a removableelectrode are not required. Instead, the lead frame can be connecteddirectly to an outside signal source, which may be an electrode fortaking current. Thus, reliability by such a preferred embodiment isexcellent.

[0030] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that a metal substrate for thermalradiation is further formed on the face opposite to the face to whichthe lead frame is adhered to the thermally conductive substrate. By sucha preferred embodiment, thermal resistance can be further decreased andthe mechanical strength is improved.

[0031] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that a printed circuit board havingtwo or more wiring layers be integrated into a part of the face of thethermally conductive substrate to which the lead frame is adhered, thethermally conductive substrate be filled to the surface of the leadframe, and the printed circuit board comprises two or more wiringlayers. By such a preferred embodiment, the control circuit forovercurrent protection or temperature compensation can be integratedinto the substrate. Thus, miniaturization and high density of theapparatus can be realized.

[0032] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the thermally conductivesubstrate has a through hole. The through hole is filled with conductiveresin composition or is plated with copper, and a metallic foil wiringpattern is formed and integrated on both sides of the substrate. By sucha preferred embodiment, double-sided wiring substrate which is excellentin thermal radiation can be obtained.

[0033] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that a plurality of the thermallyconductive substrates are layered and each thermally conductivesubstrate has a through hole. The through hole is filled with conductiveresin composition and an internal wiring pattern is composed ofconductive resin composition. In addition, a metallic foil wiringpattern is formed and integrated on both sides of the substrate. By sucha preferred embodiment, conductivity between layers of the thermallyconductive substrate is excellent and internal wiring pattern can beformed. Furthermore, excellent thermal conductivity can be provided.

[0034] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the metallic foil is a copperfoil having a thickness of 12 to 200 μm and having faces at least onesurface of which is a rough surface.

[0035] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the conductive resin compositioncomprises 70 to 95 weight parts of at least one metallic powder selectedfrom the group consisting of silver, copper and nickel; and 5 to 30weight parts of thermosetting resin and hardener.

[0036] It is preferable in the sheet for the thermally conductivesubstrate of the present invention that the inorganic filler has anaverage particle diameter of 0.1 to 100 μm.

[0037] The first method of manufacturing the sheet for the thermallyconductive substrate of the present invention comprises the steps of:forming a slurry mixture comprising 70 to 95 weight parts of aninorganic filler, 4.9 to 28 weight parts of a thermosetting resincomposition and 0.1 to 2 weight parts of a solvent having a boilingpoint of not less than 150° C. and solvent having a boiling point notmore than 100° C.; forming the slurry mixture into a film having adesired thickness; and drying the solvent having a boiling point of notmore than 100° C. of the film slurry.

[0038] The second method of manufacturing the sheet for the thermallyconductive substrate of the present invention comprises the steps of:forming a slurry mixture comprising 70 to 95 weight parts of inorganicfiller, 5 to 30 weight parts of thermosetting resin mixture comprising asolid of thermosetting resin that is solid at room temperature and aliquid thermosetting resin that is liquid at room temperature andsolvent having a boiling point not more than 100° C.; forming the slurrymixture into a film having a desired thickness; and drying only thesolvent having a boiling point of not more than 100° C. of the filmslurry.

[0039] It is preferable in the second manufacturing method that thethermosetting resin mixture in the sheet for thermally conductivesubstrate made according to the second method, comprises:

[0040] 1) 0 to 45 weight parts of resin that is solid at roomtemperature,

[0041] 2) 5 to 50 weight parts of resin that is liquid at roomtemperature,

[0042] 3) 4.9 to 45 weight parts of hardener, and

[0043] 4) 0.1 to 5 weight parts of hardening accelerator when the totalweight of the solid thermosetting resin and the liquid thermosettingresin 100 is weight parts.

[0044] It is further preferable in the second manufacturing method thatthe main component of the solid thermosetting resin is one or morecomponents selected from the group consisting of bisphenol A epoxyresin, bisphenol F epoxy resin and liquid phenol resin.

[0045] It is preferable in the first and second manufacturing methodsthat the thermosetting resin mixture comprises a brominatedmultifunctional epoxy resin as a main component, a bisphenol A novolakresin as a hardener, and an imidazole as a hardening accelerator.

[0046] It is preferable in the first and second manufacturing methodsthat the sheet for a thermally conductive substrate comprises abrominated multifunctional epoxy resin in the range of 60 to 80 weightparts; a bisphenol A novolak resin as a hardener in the range of 18 to39.9 weight parts, and an imidazole as a hardening accelerator in therange of 0.1 to 2 weight parts.

[0047] It is preferable in the first manufacturing method that thesolvent having a boiling point of not less than 150° C. is at least onesolvent selected from the group consisting of ethyl carbitol, butylcarbitol and butyl carbitol acetate.

[0048] It is preferable in the first and second manufacturing methodsthat the solvent having a boiling point of not more than 100° C. is onesolvent selected from the group consisting of methyl ethyl ketone,isopropanol and toluene.

[0049] It is preferable in the first and second manufacturing methodsthat an additive selected from the group consisting of coupling agent,dispersing agent, coloring agent and tack free agent is further added tothe sheet for a thermally conductive substrate.

[0050] It is preferable in the first and second manufacturing methodsthat the film forming method is at least one method selected from thegroup consisting of doctor blade method, coater method, and injectionmolding method.

[0051] The third method for manufacturing the thermally conductivesubstrate of the present invention comprises the steps of: piling up alead frame on a face of the sheet for the thermally conductive substratemanufactured by the first manufacturing method; molding the sheet at atemperature below the hardening temperature of the thermosetting resincomposition and at a pressure in the range of 10 to 200 Kg/cm²; fillingthe sheet and integrating to the surface of the lead frame; andhardening the thermosetting resin by thermal pressing at the pressure inthe range of 0 to 200 Kg/cm².

[0052] It is preferable in the third manufacturing method that a metalsubstrate for thermal radiation is further formed on the face oppositeto the face to which the lead frame is adhered to the thermallyconductive substrate.

[0053] Moreover, the third method for manufacturing the thermallyconductive substrate of the present invention comprises the steps of:placing the lead frame and a printed circuit board having two or morewiring layers on the sheet for the thermally conductive substratemanufactured by the method according to claim 24 in a way in which thelead frame and the printed circuit board are not overlapped; molding thesheet at the temperature below the hardening temperature of thethermosetting resin composition and at the pressure in the range of 10to 200 Kg/cm²; filling the sheet and integrating to the surface of thelead frame and the printed circuit board having two or more wiringlayers; and hardening the thermosetting resin by thermal pressing at thepressure of 0 to 200 Kg/cm².

[0054] Moreover, the third method for manufacturing the thermallyconductive substrate of the present invention comprises a series ofsteps of: processing through holes on the sheet for the thermallyconductive substrate manufactured by the method according to claim 24;filling a conductive resin composition into the through holes; piling upthe metallic foil on both sides of the sheet into which the conductiveresin composition is filled in the through holes; hardening thethermosetting resin of the sheet by thermal pressing at the pressure of10 to 200 Kg/cm²; and forming wiring pattern by processing the metallicfoil.

[0055] Moreover, the method for manufacturing the thermally conductivesubstrate of the present invention comprises the steps of: piling up ametallic foil on the both sides of the sheet for the thermallyconductive substrate manufactured by the method according to claim 24;hardening the thermosetting resin of the sheet of thermally conductivesubstrate by thermal pressing at the pressure of 10 to 200 Kg/cm²;processing through holes on the hardened the thermally conductive sheet;conducting a copper plating on the entire surface of the sheet on whichthrough holes are processed; and forming a wiring pattern by processingthe metallic foil and the copper plating layer.

[0056] Moreover, the third method for manufacturing the thermallyconductive substrate of the present invention comprises the steps of:preparing a desired number of thermally conductive substrates by thefirst manufacturing method; processing through holes at desiredlocations on each of the sheets; filling a conductive resin compositioninto the through holes; forming a wiring pattern on one surface of thefilled sheet by using the conductive resin composition; piling up eachof the sheet having the wiring pattern in a way in which the surfacehaving the wiring pattern is adjusted to face upward and the sheet onwhich only the conductive resin composition is filled to the throughhole is adjusted to be the top face to form a pile; piling up metallicfoil on both sides of the pile; hardening the thermosetting resin of thesheet for the thermally conductive substrate by thermal pressing at thepressure of 10 to 200 Kg/cm²; and forming a wiring pattern by processingthe metallic foil.

[0057] It is in the third manufacturing method that the through holesare processed by the method selected from the group consisting of laserbeam process, drilling process and punching process.

[0058] It is in the third manufacturing method that the metallic foil isa copper foil having a thickness of 12 to 200 μm and having faces atleast one surface of which is a rough surface.

[0059] It is in the third manufacturing method that the conductive resincomposition comprises 70 to 95 weight parts of at least one metallicpowder selected from the group consisting of silver, copper and nickel;and 5 to 30 weight parts of thermosetting resin and hardener.

[0060] It is in this third manufacturing method that the temperature forthe thermal pressing is in the range of 170 to 260° C.

[0061] As mentioned above, according to the present invention, highthermal radiation printed circuit wiring board for mounting electronicpower devices can be made of the thermally conductive substrate byshaping and hardening the thermally conductive sheet into a desiredshape. Shaping is possible due to the flexibility of the thermallyconductive substrate sheet, hardening makes the thermally conductivesubstrate rigid.

[0062] Moreover, according to the present invention, thermallyconductive substrate can be manufactured efficiently and reasonably.

[0063] The first embodiment of the present invention basically relatesto a thermally conductive sheet having flexibility, where an inorganicfiller is added into a thermosetting resin in the not-hardened state athigh density; the coefficient of thermal expansion in the planedirection is approximately the same as that of Si semiconductor; andhigh thermal conductivity is provided. In the thermally conductive sheetof the present invention, a high boiling point solvent is added into thethermosetting resin composition, or a thermosetting resin mixturecontaining a solid resin that is solid at room temperature and a liquidthermosetting resin that is liquid at room temperature, and films areformed by using a low boiling point solvent for mixing with inorganicfiller. Consequently, in the thermally conductive sheet of the presentinvention, inorganic filler can be added at a high filler loading.Furthermore, the flexibility of the thermosetting resin of the thermallyconductive sheet is manufactured in the not-hardened state, and, thus,molding the thermally conductive sheet into a desired shape at a lowtemperature and at a low pressure is possible. In addition, thethermally conductive substrate can be made rigid by hardening thethermosetting resin by thermal pressing. Also, a thermally conductivesubstrate on which a semiconductor can be simply and directly mountedcan be obtained by the use of this thermally conductive sheet which isflexible.

[0064] The second embodiment of the present invention relates to athermally conductive substrate on which a semiconductor having thermalradiation property can directly be mounted by using the thermallyconductive sheet; piling up a lead frame; and hardening the thermallyconductive sheet by means of thermal pressing to integrate with the leadframe.

[0065] Moreover, the third embodiment of the present invention relatesto a doubled-sided thermally conductive substrate having high thermalconductivity, which permits electrical conductivity on both sides byforming through holes on the thermally conductive sheet, filling thethorough holes with the conductive resin composition and formingmetallic foil patterns on both sides of the sheet.

[0066] Moreover, the fourth embodiment of the present invention relatesto a high thermally conductive double-sided substrate which permitselectric conductivity by copper plating to the through holes of thethird embodiment.

[0067] Moreover, the fifth embodiment of the present invention relatesto a thermally conductive substrate (a multi-layered substrate) having amulti-layered circuit structure in which a plurality of the thermallyconductive sheets are used, the through holes to which conductive resincomposition is filled are formed, wiring pattern is formed on one sideof the thermally conductive sheet, and a plurality of the thermallyconductive sheets are piled up.

BRIEF DESCRIPTION OF DRAWINGS

[0068]FIG. 1 is a cross sectional view showing a structure of thethermally conductive sheet of one embodiment of the present invention.

[0069]FIGS. 2A to 2E are cross sectional views showing each step of amanufacturing process of the thermally conductive substrate which ismanufactured by using the thermally conductive sheet of one embodimentof the present invention.

[0070]FIG. 3 is a cross sectional view of the thermally conductivesubstrate on which the thermal radiation metal substrate is furtherformed on the face opposite to face the lead frame is adhered to thethermally conductive substrate manufactured by the process according toFIG. 2.

[0071]FIGS. 4A to 4F are cross sectional views showing each step of amanufacturing process of the thermally conductive substrate which ismanufactured by using the thermally conductive sheet of one embodimentof the present invention.

[0072]FIG. 5 is a cross sectional view showing a process formanufacturing the thermally conductive multi-layered wiring substrate ofone embodiment of the present invention.

[0073]FIGS. 6A to 6J are cross sectional views showing each step of amanufacturing process of the thermally conductive multi-layered wiringsubstrate of one embodiment of the present invention.

[0074]FIGS. 7A and 7B are cross sectional views showing each step of amanufacturing process of the thermally conductive substrate of anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE IVENTION

[0075] Hereinafter, the thermally conductive substrate (single-sidedwiring substrate, double-sided wiring substrate, multi-layered wiringsubstrate) for mounting bare chip of one embodiment of the presentinvention will be explained by referring to figures.

[0076]FIG. 1 is a cross sectional view showing a structure of thethermally conductive sheet of one embodiment of the present invention.In FIG. 1, a thermally conductive sheet 100 is formed on a tack freefilm 101. The forming method includes: preparing the slurry mixturewhich comprises at least one inorganic filler, thermosetting resincomposition, a solvent having a boiling point of not less than 150° C.and a solvent having a boiling point of not more than 100° C.; andforming the mixture into a film on the tack free film 101. The filmforming method can be, for example, a doctor blade method, a coatermethod and an injection molding method can be employed. A thermallyconductive sheet having flexibility can be obtained by drying only thesolvent having a boiling point of not more than 100° C. of the filmslurry.

[0077] Moreover, similarly, a thermally conductive sheet havingflexibility can be obtained by the process comprising the steps of:preparing the slurry mixture which comprises at least one inorganicfiller, a thermosetting resin composition that is solid at roomtemperature, and a solvent having a boiling point of not more than 100°C.; forming the slurry mixture into a film on the tack free film 101,similar to the above; and drying the solvent.

[0078] The examples of the thermosetting resin include, epoxy resin,phenol resin and cyanate resin. Moreover, the examples of the inorganicfiller include Al₂O₃, MgO, BN, and AlN. The examples of the solventhaving a boiling point of not less than 150° C. include ethyl carbitol,butyl carbitol and butyl carbitol acetate.

[0079] Moreover, the examples of the thermosetting resin that is liquidat room temperature include epoxy resin such as bisphenol A epoxy resin,bisphenol F epoxy resin and liquid state phenol resin.

[0080] In addition, the examples of the solvent having a boiling pointof not more than 100° C. include methyl ethyl ketone, isopropanol andtoluene. Moreover, if necessary, coupling agent, dispersing agent,coloring agent and tack free agent can be added as an additive into thethermally conductive sheet composition.

[0081] Moreover, as mentioned above, the half hardened or partiallyhardened sheet for the thermally conductive substrate having a moderatedviscosity (10² to 10⁵ Pa·s) can be obtained by adding the solvent havinga boiling point of not less than 150° C. or adding the thermosettingresin that is liquid at room temperature, and drying the solvent havinga boiling point of not more than 100° C. If the viscosity is not morethan 10² Pa·s, the adhesion of the sheet is so strong that it isdifficult to be peeled apart from the tack free film and furthermorechanging the shapes after the process is large and the operationefficiency is bad. It is preferable that the viscosity is in the rangeof 10³ to 10⁴ Pa·s in the view of the operation efficiency andprocessing property.

[0082] Since high filler loading (ie., high filler content) in thethermally conductive substrate using this thermally conductive sheet ispossible in the present invention, the coefficient of thermal expansionof the substrate can be made to be approximately the same as that of asemiconductor, and furthermore the substrate can be made to haveexcellent thermal radiation.

[0083]FIGS. 2A to 2E are cross sectional views showing each step of amanufacturing process of the thermally conductive substrate manufacturedby using the thermally conductive sheet 100. In FIG. 2A, numeral 200denotes the thermally conductive sheet manufactured by the above method;201 of FIG. 2B denotes a lead frame forming a wiring. The lead frame 201can be obtained by punching a copper plate into a desired shape, or canbe formed by an etching method. A processed lead frame whose surface isplated with nickel prevent oxidation of copper is generally used.

[0084]FIG. 2C shows a structure in which the lead frame 201 and thethermally conductive sheet 200 are piled up.

[0085]FIG. 2D shows a structure in which the lead frame and thermallyconductive sheet are thermally pressed. Then the thermally conductivesheet is filled to the surface of the lead frame by using theflexibility of the thermally conductive sheet. Finally, thethermosetting resin in the thermally conductive sheet is hardened. Then,FIG. 2E shows the hardened thermally conductive substrate in which theportion except the necessary portion of the lead frame of the thermallyconductive substrate is cut. In FIG. 2E, the hardened thermallyconductive substrate is bent perpendicularly so as to form a removableelectrode. Thus, as described above, a thermally conductive substrate ismanufactured. Subsequently, steps of mounting parts by soldering orfilling insulating resin are carried out, but they are not importantherein and omitted.

[0086]FIG. 3 shows a structure in which the thermal radiation metalsubstrate 302 is further formed on the face opposite to the portionwhere the lead frame is adhered to the thermally conductive substratemanufactured by the steps illustrated in FIG. 2.

[0087]FIGS. 4A to 4F show the method for forming a thermally conductivesubstrate having a double-sided wiring, which is different from theabove mentioned method. FIG. 4A shows the thermally conductive sheet 400formed on the tack free film 401. In FIG. 4B, the through holes 402 isformed from the side of the tack free film 401 of the thermallyconductive sheet 400. The formation of the through holes can beconducted by a laser processing method using carbon dioxide, excimer orthe like, or by a metal molding process, or furthermore, by drilling.Punching by using laser beam is preferred, because punching holes at afine pitch is possible and scrapings are not generated. In FIG. 4C, theconductive resin composition 403 is filled into the through hole 402. Asa conductive resin composition, for example, a conductive paste formedby mixing copper powder, epoxy resin and hardener of epoxy resin can beused. In FIG. 4D, the metallic foils 404 are further piled up on bothsides of the thermally conductive sheet. FIG. 4D is thermally pressed inthis state, and the thermally conductive sheet is hardened as shown inFIG. 4E. Finally, the metallic foil applied onto both sides areprocessed as shown in FIG. 4F, and thereby the wiring pattern 405 can beobtained. Thus, the thermally conductive substrate having wiringpatterns on both sides of the thermally conductive sheet can beobtained. At this time, the lead frame can be used instead of themetallic foil. In this case, the last step, namely, the step for formingwiring pattern can be omitted.

[0088]FIG. 5 is a cross sectional view of the thermally conductivesubstrate, where the method of electrically connecting both sides of thethermally conductive substrate manufactured by the process of FIG. 4 isconducted not by the use of conductive resin composition but byprocessing through holes after hardening by thermal pressing, followedby connecting the inside layers by the copper plating method. Numeral501 denotes a copper plating layer formed on the inside surface of thethrough hole; 502 denotes a wiring pattern; and 500 denotes thethermally conductive substrate wherein the thermally conductive sheet ishardened.

[0089]FIG. 6 is a cross sectional view showing each step of amanufacturing process of a thermally conductive multi-layered wiringsubstrate of one embodiment of the present invention. FIGS. 6A to 6C arethe same as the thermally conductive sheet shown in FIG. 4 where throughholes are processed on the thermally conductive sheet and a conductiveresin composition is filled into the through holes. FIGS. 6D, 6F and 6Gshow thermally conductive sheets into which the conductive resincomposition 603 is filled and the conductive resin composition 603 isfurther used on one side thereof to produce wiring pattern 604. Themethod for forming the wiring pattern can be a screen printing method ora copper plate offset printing method or the like. In FIG. 6E, thewiring pattern by the conductive resin composition is not formed.

[0090]FIG. 6H is a pile where the thermally conductive sheets shown inFIGS. 6E to 6G are piled up as shown in the figure, and a metallic foil605 is further piled up on the both sides of the pile. FIG. 6I shows astructure in which each thermally conductive sheet is laminated,hardened and adhered by thermal pressing. FIG. 6J shows a structure inwhich the wiring pattern of the top layer 606 is finally formed. Theformation of the wiring pattern herein is carried out by an etchingmethod. The etching method is wet etching, where ferric chloride is usedas the etching reagent. Thus, a high density thermally conductivesubstrate having a multi-layered wiring structure can be obtained.

[0091] Moreover, herein, in manufacturing the printed circuit board,there are steps of applying soldering resist, printing letters or marksand punching holes for inserting parts. For these steps, however, anyconventional technique can be employed, and they are not importantherein and therefore omitted.

[0092]FIGS. 7A and 7B are cross sectional views showing each step of amanufacturing process of the thermally conductive substrate manufacturedby using the thermally conductive sheet 700. In FIG. 7A, numeral 700denotes the thermally conductive sheet manufactured by the above method;701 denotes a lead frame for forming wiring. The lead frame 701 can beobtained by punching a copper plate into a desired shape, or can beformed by an etching method. A processed lead frame whose surface isplated with nickel preventing oxidation of copper is generally used.Numeral 702 denotes the printed wiring circuit having two or more wiringlayers and it has a via 704 for electrically connecting between thewiring pattern 703 and the layers.

[0093]FIG. 7B shows a structure in which the lead frame 701, thermallyconductive sheet 700 and the printed wiring circuit 702 having twolayers or more are thermally pressed; then the thermally conductivesheet is filled to the surface of the lead frame by using theflexibility of the thermally conductive sheet; and furthermore, thethermosetting resin in the thermally conductive sheet is hardened. Then,as in FIG. 2E, the hardened thermally conductive substrate in which theportion except the necessary portion of the lead frame of the thermallyconductive substrate is cut, the hardened thermally conductive substrateis bent perpendicularly so as to form a removable electrode. Thus, athermally conductive substrate is manufactured. Subsequently, steps ofmounting parts by soldering or filling insulating resin are carried out,but they are not important herein and omitted.

[0094] Hereinafter, the present invention will be explained by referringto Examples.

EXAMPLE 1

[0095] In the formation of the thermally conductive sheet of the presentinvention; inorganic filler, thermosetting resin and solvent were mixedand alumina balls were further added into the above mixture so as toobtain a sufficient dispersion. The compositions of the thermallyconductive sheet of this Example are shown in Table 1. TABLE 1Thermosetting resin Solvent having a Sheet (including boiling point ofOther after dried Experiment Inorganic Filler hardener) not more than150° C. additives Viscosity No. Name Vol. (wt %) Name Vol. (wt %) NameVol. (wt %) *1 *2 *3 (Pa · s) 1a Al₂O₃ 60 Epoxy 36 Butyl 4 — — — 1.5 ×10² resin calbitol 1b Al₂O₃ 70 Epoxy 28 acetate 2 — — — 3.3 × 10³ resin(BCA) 1c Al₂O₃ 80 Epoxy 18 2 — — — 2.6 × 10⁴ resin 1d Al₂O₃ 90 Epoxy 9.50.5 — — — 8.1 × 10⁴ resin 1e Al₂O₃ 95 Epoxy 4.9 0.1 — — — 1.3 × 10⁵Resin

[0096] Table 1 shows an evaluation of the performance of the thermallyconductive sheet when the content of Al₂O₃ as an inorganic filler ischanged. As Al₂O₃, “AL-33” having a particle diameter of 12 μm on theaverage, the product of Sumitomo Chemical Company Limited was used; andas an epoxy resin, the epoxy resin comprising the following compositionwas used: 1) thermosetting resin main agent: 65 weight parts ofbrominated multifunctional epoxy resin (5049-B-70, the product ofYuka-shell epoxy Co., Ltd.); 2) hardener: 34.4 weight parts of bisphenolA novolak resin (152, the product of Yuka-shell epoxy Co., Ltd.); and 3)hardening acceleratoer: 0.6 weight parts of imidazol (EMI-12, theproduct of Yuka-shell epoxy Co., Ltd.). This resin composition was in asolid state and it was softened to a paste-like consistence by addingmethyl ethyl ketone. The content in the state of solid was 70%.

[0097] First, the resin compositions in Table 1 were weighed. Then,methyl ethyl ketone solvent, having a boiling point of not more than100° C. for adjusting the viscosity, was added to the compositions untilthe viscosity of the slurry became about 20 Pa·s. Subsequently, thealumina balls were added and mixed thereof in a pot with a rotating at aspeed of 500 rpm for 48 hours. At this time, the low boiling pointsolvent was used so as to adjust the viscosity of the alumina ballfilled slurry. Maintaining a low slurry-like viscosity by this slurry isimportant for adding an inorganic filler in a high concentration in theslurry. However, the low boiling point solvent was volatilized in thefollowing drying step. Since no low boiling point solvent remained inthe thermally conductive sheet composition, it is not included inTable 1. Next, a polyethylene terephthalate sheet having a thickness of75 μm was prepared as the tack free surface and the above mentionedslurry was spread out into a film by the doctor blade method with a gapof approximately 1.4 mm. Then, methyl ethyl ketone in the abovementioned film was dried by allowing the film to stand at 100° C. for anhour. Thereby, as shown in Table 1, the flexible thermally conductivesheet (the thickness was 750 μm) having a moderate viscosity wasobtained.

[0098] From the thermally conductive sheet manufactured like this, thetack free film of polyethylene terephthalate film was peeled apart.Then, the thermally conductive sheet was again covered with a thermalresistance tack free film (PPS: polyphenylene sulfite having a thicknessof 75 μm), and was hardened at the temperature of 200° C. and at thepressure of 50 Kg/cm². The PPS tack free film was peeled apart and thethermally conductive sheet was processed into a predetermined shape andsize. The thermal conductivity, coefficient of thermal expansion, breakdown voltage and flexural strength were measured. The results are shownin Table 2. TABLE 2 Evaluation of thermally conductive substrate BreakThermal Thermal Down Flexural Experiment Conductivity Expansion VoltageStrength No. (W/mK) (ppm/° C.) (kV/mm) (Kg/mm²) 1a 1.1 28 15 9.5 1b 1.224 14 12.3 1c 1.9 18 15 15.5 1d 3.5 10 12 18.8 1e 4.1 8 9 13.1

[0099] The thermal conductivity was defined by calculating thetemperature transmitted from one surface to another surface of thesample that was cut into 10 mm in size, when the sample was heated bybringing it into contact with a heater. Similarly, the break downvoltage by AC voltage shown in Table 2 was defined by measuring thebreak down voltage in the direction of the thickness of the thermallyconductive substrate and calculating the value per a unit thickness. Thebreak down voltage is affected by the adhesion between the thermosettingresin and the inorganic filler in the thermally conductive substrate. Inother words, if the wettability of the inorganic filler and thethermosetting resin was bad, micro gaps were generated between them. Asa result, the strength of the substrate and break down voltage aredeteriorated. In general, the break down voltage of a resin alone isapproximately 15 KV/mm. If the break down voltage is not less than 10KV/mm, it is judged that the adhesion between the thermosetting resinand the inorganic filler is excellent.

[0100] From the results in Tables 1 and 2, the thermally conductivesubstrate obtained by the thermally conductive sheet manufactured by theabove mentioned method had about 20 times as much thermal conductivityas the conventional glass epoxy substrate, and not less than 2 times ashigh a performance as the thermally conductive sheet manufactured by theconventional injection molding method. In addition, as to thecoefficient of thermal expansion, when the thermally conductive sheetcontained not less than 90 wt. % of Al₂O₃, the coefficient of thermalexpansion was similar to that of a silicon semiconductor. Moreover, theflexural strength of the substrate was not less than 15 Kg/mm²,exhibiting sufficient strength as substrate. Therefore, the thermallyconductive substrate of the present invention is promising as asubstrate for a flip chip on which a semiconductor is directly mounted.

[0101] Then, the performance was evaluated when the type of inorganicfiller was changed. The compositions are shown in Table 3 and theevaluation results are shown in Table 4. TABLE 3 Thermosetting resinSolvent having a Sheet (including boiling point of Other after driedExperiment Inorganic Filler hardener) not more than 150° C. additivesViscosity No. Name Vol. (wt %) Name Vol. (wt %) Name Vol. (wt %) *1 *2*3 (Pa · s) 1f Al₂O₃ 91 Epoxy 8 Butyl 0.5 0.3 0.2 — 6.1 × 10⁴ resincalbitol 1g AlN 85 Epoxy 14 acetate 0.5 0.3 0.2 — 1.6 × 10⁴ resin (BCA)1h AlN 90 Epoxy 9 0.5 0.3 — 0.2 5.8 × 10⁴ resin 1i BN 80 Epoxy 19 0.50.3 0.2 — 7.1 × 10³ resin 1j MgO 87 Epoxy 12 0.5 0.3 0.2 — 6.4 × 10⁴resin

[0102] TABLE 4 Evaluation of Thermal Conductive Substrate Break ThermalThermal Down Flexural Experiment Conductivity Expansion Voltage StrengthNo. (W/mK) (ppm/° C.) (kV/mm) (Kg/mm²) 1f 3.7  9 11 18.5 1g 4.0 11 1415.3 1h 7.4  7 5 12 13.6 1I 3.5 12 15 10.9 1j 4.2 19 10 12.0

[0103] As is apparent from Tables 3 and 4, if a powder other than Al₂O₃,for example, AlN, MgO, BN (approximately 7 to 12 μm) was used as theinorganic filler, the performance peculiar to the inorganic filler wasexhibited. In other words, if AlN having excellent thermal conductivitywas used, then the thermal conductivity similar to that of the ceramicsubstrate was obtained (Example 1h). Moreover, in a case where BN wasadded, then high thermal conductivity and low thermal expansion propertywas obtained as shown in Example 1i. At this time, the additives contentwas determined in a way in which a suitable state could be obtained inaccordance with the density and dispersion of inorganic fillers. Moreinorganic fillers can be added by adding dispersing agents such as AlN.Moreover, the thermally conductive substrate having a sufficient thermalradiation property could be obtained by coloring the thermallyconductive sheet. Moreover, as mentioned above, the addition of silanecoupling agent for improving the adhesion between the organic filler andthe thermosetting resin also improves the break down voltagecharacteristics of the thermally conductive sheet.

[0104] In Table 5, the performance of the thermally conductive sheet wasevaluated in a case where Al₂O₃ was used as the inorganic filler andresin that is liquid at room temperature was added for providingflexibility. As Al₂O₃, “AL-33” (the product of Sumitomo Chemical CompanyLimited) having an average particle diameter of 12 μm, was used; and anepoxy resin was obtained by substituting a part of NVR-1010 containing ahardener (the product of Japan REC Co., Ltd.) by liquid resin shown inTable 5. TABLE 5 Thermosetting Thermosetting resin that is resin that isSolid at room liquid at room Other Sheet Inorganic Filler TemperatureTemperature Hardener additives after dried Experiment No. Name Vol. (wt%) Name Vol. (wt %) Name Vol. (wt %) Name Vol. (wt %) Name Vol. (wt %)(Pa · s) 1k Al₂O₃ 89.5 Epoxy 9 bis F 1 Sl-100 0.2 Raven 0.3 3.1 × 10⁵resin 1060 1l Al₂O₃ 89.5 Epoxy 8 bis F 2 Sl-100 0.2 Raven 0.3 1.3 × 10⁴resin 1060 1m Al₂O₃ 89.5 Epoxy 6 bis F 4 S1-100 0.2 Raven 0.3 4.4 × 10³resin 1060 1n Al₂O₃ 89.5 Epoxy 4 bis F 6 Sl-100 0.2 Raven 0.3 2.1 × 10²resin 1060 1o Al₂O₃ 89.5 Epoxy 6 bis A 4 Sl-100 0.2 Raven 0.3 6.7 × 10⁴resin 1060 1p Al₂O₃ 89.5 Epoxy 6 phenol 4 Sl-100 0.2 Raven 0.3 3.9 × 10³resin 1060

[0105] First, the compositions in Table 5 were weighed. Then, methylethyl ketone solvent, having a boiling point of not more than 100° C.for adjusting the viscosity, was added to the compositions until theviscosity of the slurry became about 20 Pa·s. Subsequently, the aluminaballs were added and mixed thereof in a pot with a mixing devicerotating at a speed of 500 rpm for 48 hours. At this time, the lowboiling point solvent was used to adjust the viscosity of the aluminaballs filled slurry. Maintaining a low slurry-like viscosity by theslurry is important for adding an inorganic filler in a highconcentration in the slurry. However, the low boiling point solvent wasvolatilized in the following drying step. Since no low boiling pointsolvent remained in the thermally conductive sheet composition, it isnot included in Table 1. Next, a polyethylene terephthalate sheet havingthe thickness of 75 μm was prepared as the tack free surface and theabove mentioned slurry was spread out into a film by the doctor blademethod with a gap of approximately 1.4 mm. Then, methyl ethyl ketone inthe above mentioned film was dried by allowing to stand at 100° C. foran hour. Thereby, as shown in Table 5, the flexible thermally conductivesheet (the thickness was 750 μm) having a moderate viscosity wasobtained by adding a resin that is liquid at room temperature.

[0106] From the thermally conductive sheet manufactured like this, thetack free film of polyethylene terephthalate film was peeled apart.Then, the thermally conductive sheet was again covered with a thermalresistance tack free film (PPS: polyphenylene sulfite having a thicknessof 75 μm), and was hardened at the temperature of 200° C. and at thepressure of 50 Kg/cm². The PPS tack free film was peeled apart and thethermally conductive sheet was processed into a predetermined shape andsize. The thermal conductivity, coefficient of thermal expansion, breakdown voltage and flexural strength were measured. The results are shownin Table 6. TABLE 6 Evaluation of Thermally conductive Substrate BreakThermal Thermal Down Flexural Experiment Conductivity Expansion VoltageStrength No. (W/mK) (ppm/° C.) (kV/mm) (Kg/mm²) 1k 3.6 14 12 11.3 1l 3.713 14 13.5 1m 3.9 13 14 15.5 1n 4.1 15 15 17.8 1o 3.6 14 15 14.3 1p 3.913 15 18.9

[0107] As is apparent from Table 6, flexibility could be provided to thethermally conductive sheet by adding the resin that was liquid at roomtemperature. Moreover, the performance peculiar to inorganic filler wasexhibited. As compared with the method of the above mentioned Examplewhere a high boiling point solvent was added, the break down voltage byvoid and the flexural strength were excellent, because no solventexisted in the sheet at the time of molding the thermally conductivesheet.

EXAMPLE 2

[0108] In this Example, a thermally conductive substrate in which thethermally conductive sheet was manufactured by the same method as inExample 1 and integrated with a lead frame will be explained. Thecompositions of the thermally conductive sheet used in this Example willbe described hereinafter.

[0109] (1) Inorganic filler: 90 weight % of Al₂O₃, “AS-40®” (the productof SHOWA DENKO K.K.) having a spherical shape and an average particlesize of 12 μm.

[0110] (2) Thermosetting resin: 9 weight % of cyanate ester resin,“AroCy M30®” (the product of Asahi-Ciba CO., Ltd.)

[0111] (3) Solvent having a boiling point of not less than 150° C.: 0.5weight % of butyl carbitol. (the first grade of chemical reagent ofKanto Chemical CO, Inc.).

[0112] (4) Other additives: 0.3 weight % of “Carbon Black” (the productof Toyo-carbon CO., Ltd.), and 0.2 wt. % of dispersing agent, “PLYSURFF-208F®” (the product of DAI-ICHI SEIYAKU KOGYO CO., LTD.).

[0113] A thermally conductive sheet (a thickness was 770 μm) comprisingthe above mentioned compositions was used. As the lead frame, a copperplate having a thickness of 500 μm which was processed by the etchingmethod and further applied with nickel plating was piled up andthermally pressed at the temperature of 110° C. and pressed at thepressure of 60 Kg/cm². By such a process, the thermally conductive sheetflowed into gaps of the lead frame and was filled to the surface of thelead frame to form a structure as shown in FIG. 2D. Then, the thermallyconductive sheet with which the lead frame was integrated was heated bya drier at 175° C. for one hour, and thermosetting resin of thethermally conductive sheet was hardened. Such process could be conductedfor a short time by only conducting the molding at low temperature, andthe hardening could be conducted as a whole after molding, so that masstreatment in a short time was realized as an entire process. Moreover,as shown in FIG. 2E, the outer circumference of the lead frame was cutand the bending of the terminal was conducted, to thus completely formthe thermally conductive substrate. Moreover, in the above, the moldingprocess and the hardening process were separately conducted. However, aseries of process from thermal molding with pressing to hardening couldbe continuously conducted.

[0114] When the thermal conductivity of the thermally conductivesubstrate obtained as above was evaluated, the value was 3.7 W/mK.Consequently, about 2 times as high a performance as that of aconventional injection molding method or metal substrate could berealized. Moreover, for the evaluation of reliability, a reflow test wasconducted at the maximum temperature of 260° C. for 10 seconds. At thistime, there were no abnormalities at the interface between the substrateand lead frame, thus indicating a strong adhesion at the interference.

EXAMPLE 3

[0115] In this Example, a thermally conductive substrate will beexplained, where the thermally conductive sheet was manufactured by thesame method as in Example 1 and both sides of the sheet had metallicfoil wiring layers and conductive resin composition was filled betweenthe layers to electrically connect the layers. The compositions of thethermally conductive sheet used in this Example will be describedhereinafter.

[0116] (1) Inorganic filler: 90 weight % of Al₂O₃, “AS-40®” (the productof SHOWA DENKO K.K.) having a spherical shape and an average particlesize of 12 μm.

[0117] (2) Thermosetting resin: 9 weight % of “NRV-1010®” (the productof Japan REC CO., Ltd.), a mixture comprising 60 weight parts ofbrominated multifunctional epoxy resin as a main agent, 39.5 weightparts of bisphenol A nobolak resin as a hardener, and 0.5 weight partsof imidazol as a hardening accelerator.

[0118] (3) Solvent having a boiling point of not less than 150° C.: 0.5weight % of butyl carbitol (the first grade chemical reagent of KantoChemical Co, Inc.).

[0119] (4) Other additives : 0.3 weight % of “Carbon Black” (the productof Toyo-carbon CO., Ltd., and 0.2 wt. % of coupling agent, “Plen-actKR-55®” (the product of AJINOMOTO CO., INC).

[0120] A thermally conductive sheet having the tack free filmmanufactured from the above mentioned compositions and was cut into apredetermined size with through holes having a diameter of 0.15 mmpunched in it by the use of carbon dioxide laser. The through holes wereequally spaced at a pitch of 0.2 to 2 mm from the surface of the tackfree film (FIG. 4B).

[0121] A conductive resin composition for filling via hole 403,containing 85 wt. % of spherical shaped copper metal powder, 3 wt. % ofbisphenol A epoxy resin (Epikote 828, the product of Yuka-shell epoxyCo., Ltd.) as the resin composition , 9 wt. % of glycidyl ester systemepoxy resin (YD-171, the product of Tohto Kasei Co., Ltd.), and 3 wt. %of amine adducts hardener (MY-24, the product of AJINOMOTO CO., INC)were kneaded with three rolls, and filled in the through holes by thescreen printing method (FIG. 4C). After the polyethylene terephthalatefilm 401 was removed from the thermally conductive sheet to which thepaste was filled, a copper foil having a thickness of 35 μm and a roughsurface on one surface was adhered in a way in which the rough surfacefacing the side of the thermally conductive sheet. Subsequently, thethermally conductive sheet was thermally pressed at the pressingtemperature of 180° C. and at the pressure of 50 kg/cm² for 60 minutesto form a double-sided thermally conductive substrate (FIG. 4E).

[0122] By such a process, epoxy resin of the thermally conductive sheetwas hardened and a strong adhesion to the rough surface of the copperfoil was obtained. At the same time, epoxy resin in the conductive resincomposition 403 was also hardened and mechanically and electricallyconnected with both sides of the copper foil through the inner via holeconnection.

[0123] The copper foil of this double-sided copper plated board wasetched by means of an etching technique and a double sided wiringsubstrate, having a circuit on which an electrode pattern and a wiringpattern with a diameter of 0.2 mm were formed on the inner via holes,was obtained. When the thermal conductivity and the coefficient ofthermal expansion of the thermally conductive substrate manufactured bythis method were measured, the thermal conductivity was 4.1 W/mK and thecoefficient of thermal expansion for the temperature ranges from roomtemperature to 150° C. was 10 ppm/° C., thus, exhibiting excellentproperties. The flip chip mounting of a semiconductor was conducted byusing this thermally conductive substrate. The method includes: formingAu bump on the electrode of the semiconductor device by the conventionalwire bonding method; applying adhesives containing Ag—Pd as theconductive materials on the top of this bump; bonding to the electrodepattern that was formed on the double-sided thermally conductivesubstrate by the flip chip method in which the surface of thesemiconductor device was faced downward; hardening; and further mountingwith molding resin. On the double-sided thermally conductive substratethe semiconductor manufactured as mentioned above was mounted, a reflowtest was conducted 20 times at a maximum temperature of 260° C. for 10seconds. At this time, the change in the electrical resistance valueincluding that of connection between the substrate and semiconductor wasvery small. That is, the initial connecting resistance was 35 mΩ/bumpand the connecting resistance after the test was 40 mΩ/bump.

[0124] In comparison, in a conventional glass epoxy substrate on whichthe through holes were provided at 2 mm intervals, the resistance at thebonding portion between the semiconductor and the substrate wasincreased, because the coefficient of thermal expansion of semiconductorwas different from that of the substrate, so that the reflow test endedat ten times. On the other hand, the substrate of the present inventionhas a coefficient of thermal expansion in the plane direction of thesubstrate that is similar to that of a semiconductor. Thus, the changein the resistance value as a function of the numbers of reflow tests wassmall.

EXAMPLE 4

[0125] In this Example, a thermally conductive substrate, wherein thethermally conductive sheet was manufactured by the same method as inExample 1, both sides of the sheet have a metallic foil wiring layersand through hole copper plating was filled between the layers toelectrically connect the layers, will be explained. The compositions ofthe thermally conductive sheet used in this Example will be describedhereinafter.

[0126] (1) Inorganic filler: 87 weight % of Al₂O₃, “AM-28®” (the productof SHOWA DENKO K.K.) having a spherical shape and an average particlesize of 12 μm.

[0127] (2) Thermosetting resin: 11 weight % of phenol resin, “PhenoliteVH4150®” (the product of DAINIPPPON INK AND CHEMICALS, INC.)

[0128] (3) Solvent having a boiling point of not less than 150° C.: 1.5weight % of ethyl carbitol (the first grade chemical reagent of KantoChemical Co, Inc.).

[0129] (4) Other additives : 0.3 weight % of “Carbon Black” (the productof Toyo-carbon CO., Ltd.), and 0.2 wt. % of coupling agent. “Plen-act,KR-55®” (the product of AJINOMOTO CO., INC)

[0130] After the tack free film was peeled off from the thermallyconductive sheet which was manufactured by using the above mentionedcompositions, this thermally conductive sheet was cut into apredetermined size. A copper foil having a thickness of 35 μm and arough surface on one side was adhered to the thermally conductive sheetin a way in which the rough surface was faced to the side of thethermally conductive sheet. Then this structure was thermally pressedfor 60 minutes at 180° C. and at the pressure of 50 kg/cm² to form adouble-sided thermally conductive substrate.

[0131] By such a process, phenol resin in the thermally conductive sheetwas hardened to form the strong adhesion between the rough surface ofthe copper foil and the thermally conductive sheet. Processing throughholes, having a diameter of 0.3 mm and by using the drill was conductedon the thermally conductive substrate on which the copper foil wasadhered. Moreover, a 20 μm thick copper plating was applied to theentire surface including the through holes. The copper foil of thisdouble-sided copper plated thermally conductive substrate was etched byan etching technique, and thereby a double sided substrate, on which awiring pattern can be formed, was obtained (FIG. 5). The thermalconductivity and the coefficient of thermal expansion of the thermallyconductive substrate manufactured by this method were measured and thethermal conductivity and the coefficient of thermal expansion in thetemperature ranges from room temperature to 150° C. were formed to be2.8 W/mK and 18 ppm/° C., and thus, exhibiting excellent properties.

EXAMPLE 5

[0132] Here, an example of the multi-layered wiring thermally conductivesubstrate will be explained. A plurality of the thermally conductivesheets manufactured by the same method as in Example 1 were used. Wiringlayers were provided to the plurality of the layers of the thermallyconductive sheets and they were electrically connected to the thermallyconductive sheets by using a conductive resin composition. Thecomposition of the thermally conductive sheet used in this Example willbe described hereinafter.

[0133] (1) Inorganic filler: 92 weight % of Al₂O₃, “AM-28®” (the productof SHOWA DENKO K.K.) having a spherical shape and an average particlesize of 12 μm.

[0134] (2) Thermosetting resin: 7.3 weight % of cyanate ester resin“BT2170®” (the product of the Mitsubishi Gas Chemical Company, Inc.)

[0135] (3) Solvent having a boiling point of not less than 150° C.: 0.2weight % of ethyl carbitol (the first grade chemical reagent of KantoChemical CO, Inc.).

[0136] (4) Other additives: 0.3 weight % of “Carbon Black” (the productof Toyo-carbon CO., Ltd.) and 0.2 wt. % of coupling agent “Plen-act,KR-55®” (the product of AJINOMOTO CO., INC).

[0137] A thermally conductive sheet 600 comprising the above mentionedcompositions and having a tack free film polyethylene terephthalate 601was used. From the side of the polyethylene terephthalate film, which ison one side of this thermally conductive sheet, through holes 602 havinga diameter of 0.15 mm were formed at an equal spaced pitch of 0.2 to 2mm by the use of a carbon dioxide laser (FIG. 6). A conductive resincomposition 603 containing 85 wt. % of copper metal spherical shapedpowder, 3 wt. % of bisphenol A epoxy resin (Epikote 828, the product ofYuka-shell epoxy Co., Ltd.) as the resin composition, 9 wt. % ofglycidyl ester system epoxy resin (YD-171, the product of Tohto KaseiCo., Ltd.) and 3 wt. % of amine adducts hardener (MY-24, the product ofAJINOMOTO CO., INC) as a hardener was kneaded by three rolls and filledin the through hole 602 by the screen printing method.

[0138] Moreover, the tack free film 601 was peeled apart. A conductiveresin composition for forming wiring pattern containing 80 wt. % of theneedle-like Ag powder, 10 wt. % of bisphenol A epoxy resin (Epikote 828,the product of Yuka-shell epoxy Co., Ltd.) as the resin composition. 2wt. % of amine adducts hardener (MY-24, the product of AJINOMOTO CO.,INC) as the hardener, and 8 wt. % of turpentine oil as a solvent, waskneaded by three rolls and filled to the portion where the tack freefilm 601 was peeled apart by the screen printing method (FIG. 6D). Twoother thermally conductive sheets on which wiring patterns were formedwere prepared by the similar process (FIGS. 6F and 6G). In addition, bythe same method, a thermally conductive sheet, where the conductiveresin composition 603 was filled in the through holes 602 (FIG. 6E), wasprepared and piled up in a way in which the thermally conductive sheetwas made to be at the top by adjusting places as shown in FIG. 6H. Ontothe outer most layer, a copper foil of 18 μm thickness and having arough surface on one side. The laminate of this thermally conductivesheet was thermally pressed for 60 minutes at a temperature of 180° C.and a pressure of 50 Kg/cm² to form a multi-layered thermally conductivesubstrate.

[0139] The copper foil of the multi-layered thermally conductivesubstrate was etched by an etching technique to form a wiring pattern.Since this multi-layered thermally conductive substrate used copper foilfor the outer most layer portion, mounting of parts by means ofsoldering was possible. Moreover, on an inner layer, a wiring patternwas formed by the screen printing method. A line having a width of about50 μm and inner via holes could be formed by a conductive resincomposition. Thus, a high density wiring was possible, which makes thismulti-layered thermally conductive substrate very promising as asubstrate for mounting high density electrical circuits. When thethermal conductivity and the coefficient of thermal expansion of thethermally conductive substrate manufactured by this method weremeasured, the thermal conductivity was 4.5 W/mK and the coefficient ofthermal expansion in the temperature range from room temperature to 150°C. was 8 ppm/° C., thus, showing good results.

[0140] Then, similar to the above, by using the flip chip mounting of asemiconductor, the thermally conductive substrate was evaluated as amulti-chip module. The method includes: forming Au bump on the electrodeof the semiconductor device by the conventional wire bonding method;applying adhesives containing Ag—Pd as the conductive material on thetop of this bump; bonding to the electrode pattern formed on thethermally conductive substrate by a flip chip method in which thesurface of the semiconductor device was faced downward; hardening; andmounting with molding resin. On the thermally conductive substratesemiconductor was mounted, and a reflow test was conducted 20 times at amaximum temperature of 260° C. for 10 seconds. At this time, the changein the electrical resistance value including that of the bonding betweenthe substrate and semiconductor was recognized to be very stably small.That is, the initial connecting resistance of 34 mΩ/bump was onlychanged to 37 mΩ/bump after the test.

[0141] In addition, when the certain current was flowed to the mountedsemiconductor chip through the substrate of the present invention and 1W of heat was continuously generated, the change of the electricalresistance value including that of the bonding between substrate andsemiconductor was measured. In the substrate of the present invention,the change in the resistance value was insignificant in respective ofthe number of inner via holes.

[0142] Moreover, in the above mentioned Examples 1 to 5, copper andsilver particles were used as the conductive filler in the conductiveresin composition. However, in the present invention, the conductiveparticles are not limited to copper particles and other metal particlescan be used. In particular, when nickel is used, a high electricconductivity in the conductive portion can be maintained.

[0143] As mentioned above, the thermally conductive sheet of the presentinvention can be used for a thermally conductive substrate, where aninorganic filler can be added at a high filler content into athermosetting resin which is in the not-hardened state; the coefficientof thermal expansion in the plane direction is approximately the same asthat of a semiconductor; and the high thermal conductivity can beprovided. In the thermally conductive sheet of the present invention, ahigh boiling point solvent can be added or a thermosetting resin that isliquid at room temperature can be used. In the thermally conductivesheet of the present invention, an inorganic filler can be added at ahigh fiber content while flexibility of the thermosetting resin in thethermally conductive sheet is maintained in the not-hardened state, andmolding the thermally conductive sheet into a desired shape at lowtemperature and low pressure is possible. In addition, a substrate canbe made rigid by hardening the thermosetting resin by a thermalpressing. The thermally conductive substrate on which a semiconductorcan be simply and directly mounted can be obtained by the use of thisflexible, thermally conductive sheet. Furthermore, in a thermallyconductive sheet in which the above mentioned thermally conductive resinwas mixed with a thermosetting resin that is liquid at room temperaturethere existed no solvent in the sheet since the drying of the solvent ofnot more than 100° C. had already been completed. Therefore, when thissheet is heated and hardened, voids are not generated. Consequently, itsthermal conductivity is excellent and insulating property is alsoexcellent.

[0144] The thermally conductive substrate of the present invention canrealize a thermally conductive substrate on which a semiconductor havingthermal radiation property can directly be mounted by using thethermally conductive sheets by piling up a lead frame, and hardening thethermally conductive sheet by means of thermal pressing to integratewith the lead frame.

[0145] Moreover, the thermally conductive substrate of the presentinvention can realize a doubled-sided thermally conductive substratehaving a high thermal conductivity. This structure permits electricalconductivity on both sides by forming through holes in the thermallyconductive sheet, and filling the thorough holes with a conductive resincomposition. Then, metallic foil patterns can be formed on both sides ofthe sheet.

[0146] Moreover, the thermally conductive substrate of the presentinvention can realize a high thermally conductive double-sided substratewhich permits electric conductivity by copper plating to the throughholes of the third embodiment.

[0147] Moreover, the thermally conductive substrate of the presentinvention can realize a thermally conductive substrate which is amulti-layered substrate having a multi-layered circuit structure inwhich a plurality of the thermally conductive sheets are used, throughholes to which conductive resin composition is filled are formed, awiring pattern is formed on one side of the thermally conductive sheetand a plurality of the thermally conductive sheets are piled up.

[0148] As mentioned above, since the thermally conductive substrate (thesubstrate having a single-sided wiring structure, double-sided wiringstructure, and multi-layered wiring structure) using the thermallyconductive sheet of the present invention can be filled with aninorganic filler at a high filler content, it has high thermalconductivity that cannot be obtained in the case where the usual printedcircuit board is used. Moreover, since the thermally conductive sheethas flexibility and can be molded and processed into any shape, thesubstrate can be manufactured by a simple process. This case ofmanufacturing is extremely effective from an industrial viewpoint.Furthermore, the hardened substrate is rigid and mechanically strong,and it has the thermal conductivity and the coefficient of thermalexpansion equal to that of a semiconductor. Therefore, the thermallyconductive substrate of the present invention is a promising materialfor using as a power circuit substrate, which will be increasingly usedin the future, or as a substrate for mounting a digital high speedsignal processing LSI in which there occurs a loss of high power. Inaddition, it is effective as a multi chip module (M&M) or chip sizepackage (SP) for mounting flip chip where the semiconductors aredirectly mounted.

[0149] Finally, it is understood that the invention may be embodied inother specific forms without departing from the spirit or essentialcharacteristics thereof. The embodiments disclosed in this applicationare to be considered in all respects as illustrative and notrestrictive, so that the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. A sheet mixture for a thermally conductivesubstrate comprising 70 to 95 weight parts of an inorganic filler and 5to 30 weight parts of a thermosetting resin composition comprising atleast one thermosetting resin, a hardener and a hardening accelerator:said sheet mixture having flexibility in a half hardened state orpartially hardened state.
 2. A sheet mixture for a thermally conductivesubstrate according to claim 1, wherein the half hardened state orpartially hardened state has viscosity in the range of 10² to 10⁵(Pa·s).
 3. A sheet mixture for a thermally conductive substrateaccording to claim 1, wherein the half hardened state or partiallyhardened state has viscosity in the range of 10³ to 10⁴ (Pa·s).
 4. Asheet mixture for a thermally conductive substrate according to claim 1,wherein 0.1 to 2 weight parts of a solvent having a boiling point of notless than 150° C. is further added to 100 weight parts of a mixture ofan inorganic filler and solid thermosetting resin composition.
 5. Asheet mixture for a thermally conductive substrate according to claim 4,wherein said solvent having a boiling point of not less than 150° C. isat least one solvent selected from the group consisting of ethylcarbitol, butyl carbitol and butyl carbitol acetate.
 6. A sheet mixturefor a thermally conductive substrate according to claim 1, wherein saidthermosetting resin composition comprises: 1) 0 to 45 weight parts of afirst resin that is solid at room temperature, 2) 5 to 50 weight partsof a second resin that is liquid at room temperature, 3) 4.9 to 45weight parts of said hardener, and 4) 0.1 to 5 weight parts of saidhardening accelerator in 100 weight parts of said thermosetting resincomposition.
 7. A sheet mixture for a thermally conductive substrateaccording to claim 6, wherein said first resin contains one or morecomponents selected from the group consisting of bisphenol A epoxyresin, bisphenol F epoxy resin and liquid phenol resin.
 8. A sheetmixture for a thermally conductive substrate according to claim 1,wherein said thermosetting resin composition is at least one resinselected from the group consisting of epoxy resin, phenol resin andcyanate resin.
 9. A sheet mixture for a thermally conductive substrateaccording to claim 1, wherein said thermosetting resin is a brominatedmultifunctional epoxy resin, said hardener is a bisphenol A novolakresin, and said hardening accelerator is an imidazole.
 10. A sheetmixture for a thermally conductive substrates according to claim 9,wherein said brominated multifunctional epoxy resin is in the range of60 to 80 weight parts; said bisphenol A novolak resin is in the range of18 to 39.9 weight parts, and said imidazole is in the range of 0.1 to 2weight parts, in 100 weight parts of said thermosetting resincomposition.
 11. A sheet mixture for a thermally conductive substrateaccording to claim 1, wherein said inorganic filler is at least one kindof filler selected from the group consisting of Al₂O₃, MgO, BN and AlN.12. A sheet mixture for a thermally conductive substrate according tocalim 1, further comprising at least one additives selected from thegroup consisting of coupling agent, dispersing agent, coloring agent andtack free agent.
 13. A thermally conductive substrate, comprising saidthermosetting resin according to claim 1 in a hardened state, whereinthe coefficient of thermal expansion is in the range of 8 to 20 ppm/° C.and the thermal conductivity is in the range of 1 to 10 W/mK and theelectrical resistance is in the range of an electric insulator.
 14. Athermally conductive substrate according to claim 13, wherein theflexural strength of said thermally conductive substrate is not lessthan 10 Kgf/mm².
 15. A thermally conductive substrate according to claim13, wherein the flexural strength of said thermally conductive substrateis in the range of 10 to 20 Kgf/mm².
 16. A thermally conductivesubstrate according to claim 13, wherein a lead frame is furtherintegrated to the thermally conductive substrate, and said thermallyconductive substrate is filled to the surface of the lead frame.
 17. Athermally conductive substrate according to claim 16, wherein a metalsubstrate for thermal radiation is further formed on the face oppositeto the face to which the lead frame is adhered of the thermallyconductive substrate.
 18. A thermally conductive substrate according toclaim 16, wherein a printed circuit board having two or more wiringlayers is integrated into one part of the thermally conductive substratenear the face to which the lead frame is adhered to the thermallyconductive substrate, said thermally conductive substrate is filled tothe surface of the lead frame and said printed circuit board has two ormore wiring layers.
 19. A thermally conductive substrate according toclaim
 13. wherein the thermally conductive substrate has a through hole,said through hole is filled with conductive resin composition or isplated with copper, and a metallic foil wiring pattern is further formedand integrated on both sides of the substrate.
 20. A thermallyconductive substrate according to claim
 13. wherein a plurality of thethermally conductive substrates are layered and each thermallyconductive substrate has a through hole, said through hole is filledwith a conductive resin composition and an internal wiring pattern iscomposed of said conductive resin composition, and a metallic foilwiring pattern is further formed and integrated on both sides of thesubstrate.
 21. A thermally conductive substrate according to claim 20,wherein said metallic foil is a copper foil having a thickness of 12 to200 μm and having faces at least one surface of which is a roughsurface.
 22. A thermally conductive substrate according to claim 20,wherein said conductive resin composition comprises: (1) 70 to 95 weightparts of at least one metallic powder selected from the group consistingof silver, copper and nickel; and (2) 5 to 30 weight parts of athermosetting resin composition comprising a thermosetting resin and aand hardener.
 23. A thermally conductive substrate according to claim13, wherein said inorganic filler has a particle diameter of 0.1 to 100μm on the average.
 24. A method for manufacturing the sheet for thethermally conductive substrate, which comprises: (1) forming a slurrymixture comprising 70 to 95 weight parts of inorganic filler, 4.9 to 28weight parts of thermosetting resin composition and 0.1 to 2 weightparts of solvent having a boiling point of not less than 150° C. andsolvent having a boiling point not more than 100° C.; (2) forming saidslurry mixture into a film having a desired thickness; and (3) dryingthe solvent having a boiling point of not more than 100° C. of said filmslurry.
 25. A method for manufacturing a sheet for a thermallyconductive substrate according to claim 24, wherein said thermosettingresin composition comprises a brominated multifunctional epoxy resin asa main component, a bisphenol A novolak resin as a hardener, and animidazole as a hardening accelerator.
 26. A method for manufacturing asheet for a thermally conductive substrate according to claim 24,wherein said brominated multifunctional epoxy resin is in the range of60 to 80 weight parts; bisphenol A novolak resin as a hardener is in therange of 18 to 39.9 weight parts, and said imidazole as a hardeningaccelerator is in the range of 0.1 to 2 weight parts, in the 100 weightparts of said thermosetting resin.
 27. A method for manufacturing asheet for a thermally conductive substrate according to claim 24,wherein said solvent having a boiling point of not less than 150° C. isat least one solvent selected from the group consisting of ethylcarbitol, butyl carbitol and butyl carbitol acetate.
 28. A method formanufacturing a sheet for a thermally conductive substrate according toclaim 24, wherein said solvent having a boiling point of not more than100° C. is one solvent selected from the group consisting of methylethyl ketone, isopropanol and toluene.
 29. A method for manufacturing asheet for a thermally conductive substrate, which comprises: (1) forminga slurry mixture comprising 70 to 95 weight parts of inorganic filler, 5to 30 weight parts in total weight of thermosetting resin that is solidat room temperature and a liquid thermosetting resin that is liquid atroom temperature and solvent having a boiling point not more than 100°C.; (2) forming said slurry mixture into a film having a desiredthickness; and (3) drying the solvent having a boiling point of not morethan 100° C. of the film slurry.
 30. A method for manufacturing a sheetfor a thermally conductive substrate according to claim 29, wherein saidthermosetting resin mixture comprises: 1) 0 to 45 weight parts of saidsolid thermosetting resin that is solid at room temperature, 2) 5 to 50weight parts of said liquid thermosetting resin that is liquid at roomtemperature, 3) 4.9 to 45 weight parts of a hardener, and 4) 0.1 to 5weight parts of a hardening accelerator when the total weight of saidsolid thermosetting resin and said liquid thermosetting resin is 100weight parts.
 31. A method for manufacturing a sheet for a thermallyconductive substrate according to claim 29, wherein the main componentof said solid thermosetting resin is one or more components selectedfrom the group consisting of bisphenol A epoxy resin, bisphenol F epoxyresin and liquid phenol resin.
 32. A method for manufacturing a sheetfor a thermally conductive substrate according to claim 29, wherein saidthermosetting resin composition comprises a brominated multifunctionalepoxy resin as a main component, a bisphenol A novolak resin as ahardener and an imidazole as a hardening accelerator.
 33. A method formanufacturing a sheet for a thermally conductive substrate according toclaim 29, wherein said brominated multifunctional epoxy resin is in therange of 60 to 80 weight parts, said bisphenol A novolak resin is in therange of 18 to 39.9 weight parts, and said imidazole as a hardeningaccelerator is in the range of 0.1 to 2 weight parts in 100 weight partsof said thermosetting resin composition.
 34. A method for manufacturinga sheet for a thermally conductive substrates according to claim 29,wherein said solvent having a boiling point of not more than 150° C. isat least one solvent selected from the group consisting of ethylcarbitol, butyl carbitol and butyl carbitol acetate.
 35. A method formanufacturing a sheet for a thermally conductive substrate according toclaim 29, wherein said solvent having a boiling point of not more than100° C. is one solvent selected from the group consisting of methylethyl ketone, isopropanol and toluene.
 36. A method for manufacturing athermally conductive substrate, which comprises: (1) piling up a leadframe on a face of the sheet for the thermally conductive substratemanufactured by the method according to claim 24; (2) molding the sheetat a temperature below the hardening temperature of the thermosettingresin composition and at the pressure in the range of 10 to 200 Kg/cm²;(3) filling the sheet and integrating to the surface of the lead frame;and (4) hardening said thermosetting resin by thermal pressing at thepressure in the range of 0 to 200 Kg/cm².
 37. The method formanufacturing a thermally conductive substrate according to claim 36,wherein a metal substrate for thermal radiation is further formed on theface opposite to the face to which the lead frame is adhered to thethermally conductive substrate.
 38. A method for manufacturing athermally conductive substrate, which comprises: (1) placing a leadframe and a printed circuit board having two or more wiring layers onthe sheet for the thermally conductive substrate manufactured by themethod according to claim 24 in a way in which said lead frame and saidprinted circuit board are not overlapped; (2) molding the sheet at thetemperature below the hardening temperature of the thermosetting resincomposition and at the pressure in the range of 10 to 200 Kg/cm²; (3)filling the sheet and integrating to the surface of said lead frame andsaid printed circuit board having two or more wiring layers; and (4)hardening said thermosetting resin by thermal pressing at the pressureof 0 to 200 Kg/cm².
 39. A method for manufacturing a thermallyconductive substrate, which comprises: (1) processing through holes onthe sheet for the thermally conductive substrate manufactured by themethod according to claim 24; (2) filling a conductive resin compositioninto said through holes; (3) piling up a metallic foil on both sides ofsaid sheet with which the conductive resin composition is filled in saidthrough holes; (4) hardening said thermosetting resin of said sheet bythermal pressing at the pressure of 10 to 200 Kg/ cm²; and (5) forming awiring pattern by processing said metallic foil.
 40. A method formanufacturing a thermally conductive substrate, which comprises: (1)piling up a metallic foil on the both sides of the sheet for thethermally conductive substrate manufactured by the method according toclaim 24; (2) hardening said thermosetting resin of said sheet ofthermally conductive substrate by thermal pressing at the pressure of 10to 200 Kg/cm²; (3) processing through holes on said hardened thermallyconductive sheet; (4) conducting a copper plating on the entire surfaceof said sheet on which through holes are processed; and (5) forming awiring pattern by processing said metallic foil and said copper platinglayer.
 41. A method for manufacturing a thermally conductive substrate,which comprises: (1) preparing a desired number of thermally conductivesubstrates manufactured by the method according to claim 24; (2)processing through holes at desired locations on each of said sheets;(3) filling a conductive resin composition to said through holes; (4)forming a wiring pattern on one surface of said filled sheet by usingthe conductive resin composition; (5) piling up each sheet having saidwiring pattern in a way in which the surface having said wiring patternis adjusted to face upward and the sheet on which only the conductiveresin composition is filled to said through hole is adjusted to be thetop face to form a pile; (6) piling up metallic foil on both sides ofsaid pile; (7) hardening said thermosetting resin of said sheet for thethermally conductive substrate by thermal pressing at the pressure of 10to 200 Kg/cm²; and (8) forming a wiring pattern by processing saidmetallic foil.
 42. The method for manufacturing a thermally conductivesubstrate according to claim 41, wherein said through holes areprocessed by the method selected from the group consisting of laser beamprocess, drilling process and punching process.
 43. The method formanufacturing a thermally conductive substrate according to claim 41,wherein the temperature for said thermal pressing is in the range of 170to 260° C.
 44. A method for manufacturing a thermally conductivesubstrate, which comprises: (1) piling up a lead frame on the sheet forthe thermally conductive substrate manufactured by the method accordingto claim 29; (2) molding the sheet at the temperature below thehardening temperature of the thermosetting resin composition at thepressure of 10 to 200 Kg/cm²; (3) filling the sheet and integrating tothe surface of the lead frame; and (4) hardening said thermosettingresin by thermal pressing at the pressure in the range of 0 to 200Kg/cm².
 45. A method for manufacturing a thermally conductive substratefurther comprising: forming a metal substrate on the face opposite tothe face to which the lead frame is adhered of the thermally conductivesubstrate according to claim
 44. 46. A method for manufacturing athermally conductive substrate, which comprises: (1) placing a leadframe and a printed circuit board having two or more wiring layers onthe sheet for the thermally conductive substrate manufactured by themethod according to claim 29 in a way in which said lead frame and saidprinted circuit board are not overlapped; (2) molding the sheet at thetemperature below the hardening temperature of the thermosetting resincomposition and at the pressure in the range of 10 to 200 Kg/cm²; (3)filling the sheet and integrating to the surface of said lead frame andsaid printed circuit board having two or more wiring layers; and (4)hardening said thermosetting resin by thermal pressing at the pressureof 0 to 200 Kg/cm².
 47. A method for manufacturing a thermallyconductive substrate, which comprises: (1) processing through holes onthe sheet for the thermally conductive substrate manufactured by themethod according to claim 29; (2) filling a conductive resin compositioninto said through holes; (3) piling up the metallic foil on both sidesof said sheet with which the conductive, resin composition is filled insaid through holes; (4) hardening said thermosetting resin of said sheetby thermal pressing at the pressure of 10 to 200 Kg/cm²; and (5) forminga wiring pattern by processing said metallic foil.
 48. A method formanufacturing a thermally conductive substrate, which comprises: (1)piling up a metallic foil on both sides of the sheet for the thermallyconductive substrate manufactured by the method according to claim 29;(2) hardening said thermosetting resin of said sheet of thermallyconductive substrate by thermal pressing at the pressure of 10 to 200Kg/cm²; (3) processing through holes on said hardened thermallyconductive sheet; (4) conducting a copper plating on the entire surfaceof said sheet on which through holes are processed; and (5) forming awiring pattern by processing said metallic foil and said copper platinglayer.
 49. A method for manufacturing a thermally conductive substrate,which comprises: (1) preparing a desired number of thermally conductivesubstrates manufactured by the method according to claim 29; (2)processing through holes at desired locations on each of said sheets;(3) filling a conductive resin composition into said through holes; (4)forming a wiring pattern on one surface of said filled sheet by the useof said conductive resin composition; (5) piling up each of said sheethaving said wiring pattern in a way in which the surface having saidwiring pattern is adjusted to face upward and the sheet on which onlythe conductive resin composition is filled to said through hole isadjusted to be the top face to form a pile; (6) piling up metallic foilon both sides of said laminate; (7) hardening said thermosetting resinof said sheet for the thermally conductive substrate by thermal pressingat the pressure of 10 to 200 Kg/cm²; and (8) forming a wiring pattern byprocessing said metallic foil.
 50. A method for manufacturing athermally conductive substrate according to claim 49, wherein saidthrough holes are processed by the method selected from the groupconsisting of laser beam process, drilling process and punching process.51. A method for manufacturing a thermally conductive substrateaccording to claim 49, wherein the temperature for said thermal pressingis in the range of 170 to 260° C.